I used one of these for a sidetone oscillator for a SR 150.?
C$7.25 | DC 9-12V XR2206 Function Signal Generator DIY Kit Sine/Triangle/Square Output 1Hz -1MHz Signal Generator? Adjustable module
I used the sine wave function and coupled it to the speaker with an electrolytic capacitor. I used a double pole relay, one pole to key the oscillator to the speaker and one to isolate the grid block from the key.?